1. Field of the Invention
This invention relates to well tool locking systems suitable for use with wireline tool strings. One aspect of the invention relates to apparatus for releasably locking a well tool such as a surface-controlled subsurface safety valve (SCSSV) in a staggered well bore. Another aspect of the invention relates to a latch assembly for use in preliminarily latching a lock mandrel inside a flow conductor in a staggered well bore.
2. Description of the Prior Art
Lock mandrels useful for releasably locking other well tools such as a wireline-retrievable SCSSV inside a flow conductor are well known. Such lock mandrels have previously been disclosed, for example, in U.S. Pat. Nos. 4,545,434 and 4,745,974. These patents teach the use of a running tool in a wireline tool string for driving a lock mandrel having a SCSSV connected to it into a landing nipple disposed in the flow conductor of a well.
The safety valve and lock mandrel are driven downwardly into the landing nipple until a fixed no-go ring on the outer surface of the lock mandrel contacts an opposing no-go shoulder in the landing nipple. The running tool is not releasable from the lock mandrel until the SCSSV has been pressured open and the locking keys have engaged the locking annulus of the landing nipple. The locking keys in the lock mandrel are engaged by jarring upwardly on the running tool. An alternative locking system is disclosed in U.S. Pat. No. 4,844,159.
Although the locking systems disclosed in U.S. Pat. Nos. 4,545,434 and 4,745,974 possess significant advantages when compared to the conventional locking systems previously known, problems have been encountered in using those locking systems when the well bore is staggered or graduated between the landing nipple and that section of the bore in which the SCSSV is set. In such situations, the control line pressure exerted to pump the safety valve open during the locking process instead forces the lock mandrel and valve assembly upward before the lock mandrel locking keys can be set due to the area differential in the two sections of the staggered bore.
In U.S. Pat. No. 4,962,813 [application Ser. No. 316,670], incorporated by reference herein, apparatus is disclosed for prepropping the locking keys into the locking annulus of the landing nipple prior to applying control line pressure to the SCSSV. With the locking keys prepropped in this manner, they are prevented from being forced upward out of alignment with the locking annulus of the landing nipple when control line pressure is applied to the SCSSV in a staggered bore. Once the SCSSV is pressured open, the core of the running tool drops and the running tool is jarred upward, causing the locking keys to fully engage the locking annulus. The running tool is then released from the lock mandrel, and can be withdrawn from the well bore.
Notwithstanding the advantages achieved by use of the apparatus disclosed in U.S. Pat. No. 4,962,813 [application Ser. No. 316,670], however, operational considerations suggest that alternative means may be even more desirable for securing the lock mandrel in its preferred alignment with the locking annulus of the landing nipple until the SCSSV is activated and the locking keys are fully engaged.